Exhaust valve stem oil seals.

[Joeck]

I am currently refurbishing a 1098 cylinder head which is fitted with the more modern valve stem oil seals to both inlet and exhaust.

I wonder what the consensus is on the re fitting of the new type seals to the exhaust valves ?

I have spent some time ensuring that the rocker oil feed has a clear passage from the head via No1 rocker shaft by machining a small groove to connect the mis alignment, so I expect that there should be good top end lubrication.
Joe.

[philthehill]

I would suggest that the new style of top hat valve stem seals should not be fitted to the exhaust valve guides. Unleaded petrol has no lubrication qualities. Therefore the exhaust valve stems need all the lubrication they can get otherwise there is a possibility of the valve stem sticking in the guide.
The new style top hat valve stem seal can be fitted to the inlet valve guide as they are effective in keeping oil from passing down the guide into the inlet manifold so causing the engine to smoke.
You should use the valve guides with top hat seal retention groove.
As regards the old ex factory style of valve stem oil seal they can be thrown in the bin as they are absolutely useless in keeping oil away from the inlet valve/guide/inlet manifold.
The valve guide shroud and flat seal can also be thrown in the bin. BMC discarded the shroud and flat seal as they were totally ineffective in doing their job in keeping oil away from the inlet manifold.
I have also had to enlarge the hole at the bottom of the No: 1 rocker pillar because the holes were not fully aligned.

Rocker pillar 2.jpg (27.05 KiB) Viewed 3941 times

[oliver90owner]

Agree with Phil. In the mid 1970s I had an exhaust valve that hung open, when hot, on a head that had been seriously modded. I can’t remember whether the head was removed and reamed or whether removing the stem seal fixed it. Valves with over-sized stems were fitted, in those days, as guides were not fitted to Ford heads. I’ve never fitted stem seals on exhaust valves since.

[Joeck]

Many thanks for your prompt replies, it’s much appreciated.
I will leave out the seals on the exhaust valves.

There was quite a misalignment of the oil feed holes which I managed to “plot” by using engineers blue and then grind a passageway to suit.

Am I correct in thinking that the underside face of the rocker pillar and the cylinder head pillar face are an effective seal for the oilway to the rockers when fully tightened ?

[oliver90owner]

Am I correct in thinking that the underside face of the rocker pillar and the cylinder head pillar face are an effective seal for the oilway to the rockers when fully tightened ?

Sufficient as long as the surfaces are not seriously damaged (highly unlikely).

There is no fully effective seal, but it is simply not required - there is very little pressure at that point and the oil flow will be far more than any tiny leakage that might occur. That tiny leakage (if any) isn’t going anywhere where it shouldn’t!

It would be like comparing the flow rates of a slowly dripping tap with the tap turned on fully. Or the differences in pressure across inlet valve guides and the exhaust valves - inlet has a fairly good vacuum when the throttle is closed during normal driving but the exhaust gases are just speeding along the exhaust manifold and silencer with as little back-pressure as possible.

[philthehill]

As above - there is no requirement to have any form of sealing between the head and the bottom of the rocker pillar.

[Joeck]

Many thanks chaps.
I have checked both faces and, apart from fine machining lines, they both appear to be in fine order.
I will hopefully get the head finished this weekend and soon will be starting the same rebuild process on the engine block. Should be interesting and I am sure there will be many more questions.
Thanks again.
Joe.